Electrode joint



y 1959 H. v. JOHNSON 2,894,776

ELECTRODE JOINT Filed Aug. 12, 1954 United States Patent fliice2,894,776 Patented July 14, 1959 ELECTRODE JOINT Harry V. Johnson,Niagara Falls, N .Y., assignor to Union Carbide Corporation, acorporation of New York Application August 12, 1954, Serial No. 449,3746 Claims. (Cl. 287-127) This invention relates to an electrode joint,especially one of the sort used for large furnace electrodes, and hasfor an object to reduce the danger of breakage in a threaded nipplejoining two electrode sections.

This application constitutes a continuation-in-part of application,Serial No. 300,243, filed July 22, 1952, now abandoned.

A precise analysis of the stresses in such a joint has not been possiblebecause of the high temperature within a furnace when any rupture mayoccur. Vibration, thermal and mechanical shock, and other causes havebeen considered in striving to diagnose the cause of any rupture in thenipple. My diagnosis has pointed to the conclusion that flexure is animportant factor. The closest known prior art construction is that ofPatent No. 2,510,230 dated June 6, 1950 for Electrode Joint, of which Iwas one of the joint inventors. This was perhaps too stiff at thenipple. In that construction, pitch on being heated, melted and filledthe clearance spaces between nipple threads. On further heating thepitch carbonized, acting as a binder to hold the nipple and electrodesections against becoming loosened or unscrewed.

According to the present invention, the hazard of possible nipplefailure has been reduced, not by strengthening the nipple, but byshielding it and causing more of the flexural impact stresses to betransmitted directly between electrode sections and without passingthrough the nipple. More specifically, the end faces of the electrodesections are bonded by pitch filling the pores and crevices in the endfaces while these end faces are in good mechanical and electricalcontact. Also the clearance spaces between the threads of the nipple andelectrode sections are left free, uncemented, and unfilled by pitch. Inthis way very slight tilting or sliding of the contacting threads of thenipple and electrode may occur as impact flexure is transmitted betweenthe electrode sections. If the face bond should break on the tensionside under flexural impact, the localized nipple stresses are notexcessive.

In the accompanying drawing:

Fig. 1 is an elevation view partly in section of an electrode jointembodying this invention. Fig. 2 is an enlarged detail of a modificationof Fig. 1. Fig. 3 is a view similar to Fig. 1 showing in partial sectionanother embodiment of the invention. Fig. 4 is a detail showing theclearance spaces between threads of the electrode joint of Fig. 1whichare not filled with pitch.

The invention is an electrode joint comprising a pair of electrodes eachhaving a conventional cavity for reception of a customary nipple, and,additionally, at least one of such electrodes having a recess on an endface into which is placed a carbonizable material, such as pitch, whichupon heating becomes liquid and then changes to a carbon residue, actingas a binder.

Referring to the drawing, Fig. 1 illustrates an electrode jointembodying the invention comprising an upper electrode section 10, alower electrode section 11, and

a threaded nipple 13, all constructed of carbonaceous electrodematerial. The upper section 10 is provided with a threaded socket 14 toreceive the upper end of the nipple 13, and the lower section 11 has asimilar threaded socket 15 to receive the lower end of the nipple 13. Inthe lower end face 16 of the upper section iii is an annular recess orreservoir 17 filled with pitch. As the electrodes become heated duringuse, this pitch melts and flows into the natural crevices and poresadjacent to the recess 17, and upon further heating carbonizes to form astrong, electrically conductive bond between the abutting end faces ofthe electrode sections.

In the embodiment of the invention illustrated in Figs. 2 and 3, Figure2 representing a modification of Figure 1 and showing an annular recess29 in a lower electrode section instead of a recess in the uppersection, an electrode joint comprises an upper electrode section 20, alower electrode section 22, each having conventional sockets 24, 26,respectively, for reception of a usual nipple 27. In the upper end face28 of the lower section 22 is an annular recess 29 and in the lower endface 30 of the upper section 20 is an annular recess 31 out of registerwith the recess 29. Both of the recesses 29, 30, are filled withcarbonizable material. In this joint there are thus provided two bondsbetween abutting end faces of the electrodes. Although gravity may notbe expected to cause pitch to flow out of the reservoir shown in theupper end face of a lower electrode section, nevertheless on heating,expansion and foaming will cause considerable pitch to overflow from therecess 29.

Electrode joints embodying the invention are strong after heating andresist loosening during service. Tests have shown that the joint is notloosened by the application of twice the torque applied in assemblingthe sections. In addition to greater strength, the joint of theinvention has better electrical properties than unbonded joints in thatits electrical resistance is lower.

The carbonizable material that is most generally satisfactory for use inthe invention is coal tar pitch having a melting point of about C. to175 C. In tests conducted in a production run on steel melting furnacesusing 20 inch diameter graphite electrodes, joints of the typeillustrated in Fig. l were utilized. The recess in the end face of theupper electnode section was /2 inch wide and M3 inch deep. When filledthis recess takes about 0.85 pound of pitch. It was filled with a coaltar pitch having a melting point of C. The end face area renderedunavailable for bonding by the mouth of the recess is not more thanabout 6% to 15% of the entire area of the end face. This pitch recessshould be about 1% inches from the nipple and about 2%. inches from theouter edge of the end face. Over the test period the joint of theinvention was satisfactory, no loosening occurred, and no joint wasbroken. The pitch recess is placed nearer the nipple than to theelectrode periphery in order that the recess will not become exposed byoxidation of the periphery until the joint reaches or approaches thearc.

Fig. 4 shows the inevitable clearance spaces 32 which exist at thethreads of the nipple. If there were no clearance spaces at each end ofthe nipple it would be impossible, without great expense, to have thebottom of the socket in each electrode section contiguous the nipple aswell as having the end faces of each electrode section in contact. Dueto the end faces of each electrode section around the nipple being oflarger area than the base of the nipple socket in each section, it ispreferable to have the end faces in good mechanical and electricalcontact for the sake of improved conductivity. In the present inventionthe nipple may slide slightly or tilt slightly in the socket of eachsection as fiexure occurs in the electrode joint. In the present casethese clearance spaces around all nipple threads are vacant and thethreads are uncemented in order that the aforementioned sliding orslight tipping may occur unimpeded. This means that less localizedflexural stresses in the joint occur in the nipple than was the ease inthe aforementioned construction of Patent No. 2,510,230 where thepresence of the pitch binder filling clearance spaces adjacent thenipple threads made the joint much stiffer, causing substantially allthe flexural stresses to be transmitted through the nipple locally. Inthat prior patent construction there was little or no bonding betweenthe end faces and any bonding that did exist was incidental andunintentional. In the present case on the other hand bonding between thecontiguous end faces of the electrode sections does exist and any smallamount of pitch that may exude from the pores and crevices in an endface into the nipple thread clearance space is no more than enough tofill only about 5 percent of the thread clearance volume adjacent theinterfaces and so small as to be immaterial and not impede the slightsliding or tilting movements referred to. In other words any slightamount of pitch which may get into the nipple thread clearance space inthe present invention is not enough to cause an objectionable amount offiexural stress to be transmitted through the nipple. When the end facesof the electrode sections are bonded, flexural stresses are transmitteddirectly between such sections without having any substantial amount ofthose stresses having to pass through the nipple. In the presentinvention it will be noted there are no longitudinal or transversepassageways formed in the nipple to facilitate the flow and spread ofpitch. In fact a much smaller quantity of pitch is used in the presentinvention than in the former patent construction.

Instead of having a wire gauze or other means to prevent the pitch ingranular form from falling out of its recess or reservoir, it has beenfound that the pitch may be cast or molded into the recess and when somolded is not in danger of falling out under the influence of gravity attemperatures Well below its melting point. A reason for the constructionof Fig. 3 is not so much to provide a better bond resulting from tworeservoirs being used than is obtainable from one reservoir as shown inFig. 1, but rather the construction of Fig. 3 is more nearly fool proofin operation, that is the electrode sections when being united by thenipple may sometimes inadvertently become connected wrong side up. It isto constitute a safeguard against this accidentally happening that theconstruction of Fig. 3 is primarily intended to be safer and avoid thepossibility of electrode sections being connected without any pitch bondbetween them.

What is claimed is:

1. In a connecting joint between sections of an electric furnaceelectrode comprising electrode sections, a nipple threaded into a socketin each section holding abutting faces of said sections in contact, theimprovement comprising at least one electrode section being provided onits face with a reservoir containing a predetermined amount ofliquefiable pitch, positioned substantially concentrically with theelectrode circumference,

said pitch being adapted upon heating to liquefy and flow from saidreservoir, inwardly and outwardly through pores and crevices in thecontiguous end faces of said joint, and upon continued heating tocarbonize and to bond such end faces and to maintain them in abuttingengagement while leaving clearance spaces between said nipple threadsand said socket largely unfilled by said pitch.

2. An electrode joint according to claim 1 in which melted pitch willflow by gravity from its recess.

3. In a process of connecting electric furnace electrode sectionscomprising threading a nipple into each section, uniting said sectionswith their end faces abutting one another while having clearance spacesadjacent the nipple threads, heating a pitch binder in just sufficientamounts to fill the area of abutting faces, in a reservoir in at leastone such section, melting and flowing said pitch from its reservoir, andcarbonizing said pitch on further heating the same to bond the surfacescontiguous to said carbonized pitch hinder, the combination therewith ofthe improvement for connecting said sections to reduce fiexural stressesin said connected sections from having to pass through said nipple, saidimprovement including locating said pitch reservoir contiguous an endface of at least one of said sections, and of a size such that only aminor portion of the area of said end face in one section outside saidnipple is taken up by said reservoir, melting the pitch in saidreservoir, causing it to flow radially outwardly and radially inwardlyfrom said reservoir in crevices and pores in the abutting end faces ofsaid sections.

4. An electric furnace electrode joint comprising a nipple threaded intosections of said electrode, at least one section of said electrode beingprovided with a recess into which a cementitious thermal setting binderis molded in suificient amount to just fill the abutting face area ofthe electrode sections, said binder being of a type adapted to be meltedon heating and capable of flowing by gravity out of said recess intopores and crevices in contacting surfaces and adapted on further heatingto thermally set and bond said contacting surfaces.

5. An electrode joint according to claim 4 in which said binder is anelectrically conductive pitch having a melting temperature between aboutC. and C.

6. An electric furnace electrode section containing a threaded axialsocket for reception of a nipple, an end face of said section around thenipple socket containing a generally circular recess, a predeterminedamount of a thermally setting binder in said recess, and said recessbeing closer to the nipple socket than to a periphery of the section,said binder being adapted to melt on becoming heated and to flow out ofsaid recess into any pores and crevices in the end face.

References Cited in the file of this patent UNITED STATES PATENTS1,008,002 Allen Nov. 7, 1911 1,743,888 Hamister Jan. 14, 1930 2,093,390Wyckofi Sept. 14, 1937 2,147,254 Hinderliter Feb. 14, 1939 2,510,230Johnson et al. June 6, 1950 FOREIGN PATENTS 351,151 Great Britain June25, 1931 new

